1. Field of the Invention
This invention relates to a multilayered-eddy-current type strong magnetic field generator which is suitable for various research works in magnetics engineering such as studies of magnetic properties of materials, in power magnetics, in bio-magnetics, and in nuclear fusion. More particularly, the invention relates to a strong magnetic field generator which can continuously generates a very strong magnetic field by superposition of eddy currents that are individually induced in multiple conductor layers respectively.
2. Related Art Statement
Much efforts are currently undertaken for research and development of strong magnetic field generators by using large-scale experimental facilities, in order to promote investigations and studies of properties of materials in strong magnetic field, preparation and testing of new materials and experiments on nuclear fusion.
Conventional strong magnetic field generators can be classified into several groups; namely, destructive pulse strong magnetic field generators such as those of KNER method and the implosion method, nondestructive pulse strong magnetic field generators such as those of the multilayered coil type and the so-called MIT type, continuous strong magnetic field generators such as those of superconductive type and hybrid type.
The strong magnetic field generators of the prior art provided very strong magnetic fields, but they have shortcomings in that the duration of the strong magnetic fields generated is very short, that special facilities such as extremely low temperature apparatus and large power source apparatus are required, that only pulse or direct-current (DC) magnetic field can be generated, and that continuous generation of strong alternating-current (AC) magnetic field is not possible.
To overcome the above shortcomings of the prior art and to facilitate continuous generation of strong AC magnetic field, the inventors proposed an eddy current type strong AC magnetic field generator in their Japanese Patent Application No. 61(1986)-228,459. More specifically, the eddy current type AC magnetic field generator which was previously proposed by the inventors uses a conductor plate placed in an AC magnetic field to be produced by an electromagnetic formed of a coil, so that an eddy current is induced in the conductor plate for generating a counter magnetic field for neutralizing the AC magnetic field of the electromagnet. A cavity is bored in the conductor plate in such a manner that the AC magnetic field due to the eddy current is converged in the cavity so as to intensify the magnetic flux density to an extremely high level at the cavity. Thereby, a very strong AC magnetic field is generated at the cavity by the converging of the eddy current thereat.
FIG. 7 and FIG. 8 show examples of the previously proposed eddy current type strong AC magnetic field generator. In FIG. 7, two conductor plates 1a and 1b with a minute slit 2 or a cavity therebetween have two coils 14a and 14b mounted on opposite surfaces thereof. When the coils 14a and 14b are excited by applying a suitable AC voltage thereto, AC magnetic flux is converged in the slit 2 due to the above-mentioned reason, and the magnetic flux density in the slit is intensified and a strong AC magnetic field is generated there.
In the example of the eddy current type strong AC magnetic field generator of FIG. 8, a conductor disk 1 with a central hole 3 and a slit 2 in radial direction is disposed within a single coil 14. The slit 2 is in the form of a notch extending from the periphery of the disk 1 to the central hole 3. In this case, the AC magnetic flux is converged at the central hole 3 due to the same reason, and a strong AC magnetic field is generated there.
However, the above eddy current type strong AC magnetic field generator has a shortcoming in that leakage of the magnetic flux to be converged is fairly large. Due to the large leakage, it has been difficult to intensify the density of the AC magnetic flux at the slit 2 or the hole 3 to a theoretical expected level. Thus, the efficiency of AC magnetic field generating has been low, and it cannot operate satisfactorily with a small power source.
More particularly, FIG. 9 shows the distribution of equi-vector-potential lines in the strong AC magnetic field generator of FIG. 7, depicting the manner in which the magnetic flux converges. FIG. 10 shows the magnetic flux distribution in the AC magnetic field generator of FIG. 7, which distribution was checked by experiments. The distributions of the equi-vector-potential lines and the magnetic flux indicate that the structure of FIG. 7 has a large leakage of magnetic flux and the convergence of the AC magnetic flux in the slit 2 is limited to a comparatively low level.
FIG. 11 shows the distribution of equi-vector-potential lines in the strong AC magnetic field generator of FIG. 8, illustrating the manner in which the magnetic flux converges. This figure also indicates a large leakage of magnetic flux as in the preceding example, which means that a high density of AC magnetic flux in the hole 3 is difficult to achieve with the structure of FIG. 8.